Admin panel: red marks in drop-down lists

Dear community, could you help me, please?
The problem is there's something wrong with drop-down lists in Admin: I cannot set filter to the category or product, and cannot set category to product - a red mark appears near the selected field and doesn't allow to save.
To test my problem I've installed OC from scratch once more, without any additional extensions, or themes, but it still happens.
OC 4.0.1.1, localhost, both in Chrome and Firefox. So right after the installation in Admin I go to Catalog - Products, open product and see these red marks near categories in links. If I try to save the product (without changing anything) - system shows error "Please check form carefully for errors" and let me save product only when I remove all categories. These are categories and products that were created in demo. Same happens with filter that were created by me.
Error log doesn't show anything.
Where is the mistake? I've tried to google, looked through forum, but hadn't found such case.
I will be very grateful for your help!

You should read the forum posts here! To repeat, OpenCart 4.0.1.1 is not suitable for a live website, it still has too many bugs. At the very least, you should try the current master branch which should have this particular bug, and others, already fixed. Still not suitable for a live site though, either.

If you plan to use OpenCart on a live website, use OpenCart 3.0.3.8, or the 3.0.x.x_Maintenance branch (which is based on 3.0.3.8 with added PHP 8.x support and some bugfixes.